This invention relates generally to communication networks and more particularly to systems for qualifying telephone lines for data transmission. As is known in the art, public switch telephone networks, i.e., so-called plain old telephone service (POTS) lines, were originally designed for voice communications, which cover a limited frequency bandwidth (i.e., about 4 KHz). Today, it is desired to use the same POTS lines for data transmission. Data signals, however, generally have different frequency characteristics than voice signals. As a result, a POTS line that works well transmitting voice signals might not work well, or may not work at all, for data signals. Telephone companies need to know which lines are suitable, i.e., qualify, and which lines are not suitable for data transmission. Telephone companies also need to know the reason why particular lines are unable to support data transmissions and where such faults occur so they can determine whether the transmission line can be corrected.
There are problems for telephone operating companies (Telco's) attempting to qualify subscriber loops for delivery of data. One problem is strategic. Telco's are reluctant to deploy emerging technologies for the delivery of data transmission services (e.g., ISDN or ADSL) because there is uncertainty in their knowledge that sufficient of the subscriber loops are of high enough quality to make deployment economically successful. This discourages early adopters because there is significant risk in being first to deliver a technology that may not work in their access network. If Telco's could be given a technology to take much of this risk out of initial deployment, they can secure market share and lead in the face of competition.
An additional problem is tactical and comes after a Telco has made a decision to deploy a particular technology. There is a need to qualify, either pro-actively or reactively, specific lines for service as that service is requested by subscribers or targeted by the Telco for delivery. There are a number of factors which decrease the end to end data transmission rate attainable on a pair of wires of a telephone line. Some of these factors are imbalanced lines, contact faults and the like. Given that a telephone line has no other parasitic conditions or noise interferers, the operation of the service on the line ultimately depends on the overall attenuation or insertion loss of the wire pair to the signal applied. Currently telephone companies measure insertion loss by deploying personnel to either end of the wire pair to measure the insertion loss at different frequencies (e.g. 100 kHz, 300 kHz, etc.) through hand held instruments. This procedure is expensive, labor intensive, and time consuming. It would be desirable to have an apparatus and method for estimating the insertion loss of a line for data transmission services, and further that the method and apparatus be simple to implement, efficient, and not require the deployment of personnel to remote locations.